Learn Spanish (Latin America): Nunca dejas de preocuparte por el futuro. - You never stop worrying about the future.

On its own, dejar usually means to leave or let. But when you use the phrase dejar de followed by an infinitive verb (like preocuparte), it means "to stop doing" something. It is a very common phrase that always uses this structure!

Why is te attached to the end of preocuparte?

Preocuparse (to worry) is a reflexive verb. Since it follows dejar de, the verb stays in its infinitive (dictionary) form, preocupar. However, you still need the reflexive pronoun to match the "you" doing the action. We attach te directly to the end, creating preocuparte. You could also put it before the conjugated verb: Nunca te dejas de preocupar por el futuro. Both are perfectly correct!

Why do we use por to say "about" the future? Wouldn't sobre make more sense?

While sobre literally means "about" or "on," the verb preocuparse is almost always followed by the preposition por when you want to say you are worrying "about" something. It is best to memorize preocuparse por as a matching pair.

Since Nunca means "never," do I need to add no to make it a double negative?